What adapter diameter do I need – M30x1.5 and other thread types on valves
What adapter diameter do I need – M30x1.5 and other valve threads
When a customer selects a programmable head and brings it home, most of them realize the problem only at the moment when they stand in front of the radiator with the head in their hand and discover that it simply won't screw on... or it does. The thread on the valve and the thread on the head do not match. This exact situation is likely the most common source of confusion and unnecessary returns we encounter in the sale of heating technology.
The topic of this article is therefore a truly detailed overview of threads and adapters used on radiator thermostatic valves – with an emphasis on helping you to know exactly what to buy after reading, without the need to call a technician or search the internet.
Why are there so many different threads in the first place?
Radiator valves are a technical component that has been developing for decades, and each manufacturer originally had its own solution. German companies such as Heimeier, Danfoss, or Oventrop defined their own standards even before international standardization became as strict as it is today. The result? Threads that are very similar but mutually incompatible became established in parallel on the market – and the customer stands in front of the radiator, turning their head in confusion.
The situation is further complicated by the fact that in older apartment buildings (panel houses, as well as masonry buildings from the 70s to 90s), valves from every corner of the then Czechoslovakia, GDR, or Soviet Union are installed. You will encounter threads that you won't find in any current catalog, but adapters for them still exist.
Today the situation has improved significantly. The M30x1.5 standard has become the de facto universal industrial standard for thermostatic heads – and the vast majority of modern programmable heads are based on it. That doesn't mean, however, that your old valve at home will fit it.
M30x1.5 – the standard that won
The M30x1.5 thread is now the most widespread format for thermostatic heads throughout Europe. What do these numbers mean? The letter M stands for metric thread, the number 30 indicates the outer diameter in millimeters, and the number 1.5 is the pitch (lead) of the thread in millimeters – that is, with each full turn, the screw advances by 1.5 mm.
This thread is used, for example, by Heimeier, Herz, Oventrop, IMI Hydronic, Comap, and today by most of the cheaper manufacturers, including Chinese OEM components. This practically means that if you buy any modern programmable head, such as Elektrobock HD10 or SALUS PH 55, they will have the basic mounting on M30x1.5.
Important detail: M30x1.5 is an external thread on the valve body, onto which the internal thread of the head nut is screwed. Some customers confuse this – the valve has a male thread on itself, the head has a female thread inside. The male thread is therefore tightened onto the valve with a nut.
How to identify M30x1.5 on your own valve
If you have a sliding caliper (micrometer) with you, measure the outer diameter of the threaded part of the valve – that part where the manual thermostatic head or protective cover used to sit. If you get a value close to 30 mm (in practice, 29.8 to 30.2 mm are common manufacturing tolerances), it is very likely M30x1.5.
If you don't have a caliper, a visual inspection can also help: valves with M30x1.5 have a relatively robust, wider thread. An older thin valve with a thread around 25–28 mm is more likely to be one of the less common formats described further below.
Overview of other threads and their occurrence in practice
The following list captures the threads that we encounter in standard installation practice. They are not ordered by frequency of occurrence, but by logical group:
Danfoss RA / RAS / RAV / RAVL – proprietary bayonet system
Danfoss is a Danish company that decided to go its own way and created an internal RA system (sometimes also marked as RA-N). This system is not a standard metric thread – it is a combination of a bayonet closure and a locking mechanism that ensures the head clicks into place with a distinct snap. There are three basic versions: RA for the older system, RAV for valves with a different body, and RAVL for valves with a low construction height.
Danfoss valves were extremely popular in new buildings from the 90s up to today, not only in Denmark, but also throughout Central Europe. You will find them very commonly in Slovak and Czech panel houses from the years 1995–2015. If you want to install, for example, Elektrobock HD20 on such a valve, you will need a Danfoss RA → M30x1.5 adapter.
The Danfoss adapter looks like a small plastic or metal ring that is snapped onto the valve and has an external M30x1.5 thread for the head. It is important to ensure that the adapter is exactly for the corresponding type of Danfoss valve – RA and RAV are not physically interchangeable despite being from the same manufacturer.
M28x1.5 – less common, but occurs
A diameter of 28 mm with the same pitch of 1.5 mm can be found, for example, on some older Comap valves or on valves from German production from the 80s. In Slovak households, it is more of an edge case, but if you measure 28 mm, don't confuse it with a manufacturing tolerance of M30 – a difference of two millimeters is clearly noticeable on a thread.
M32x1.5 – valves with a larger diameter
This thread appears, for example, on some more flow-intensive valves for larger radiators or on older Oventrop valves from a certain production period. An M32→M30 adapter exists, but it is not always easy to find. If you encounter it, you won't find it in local hobby stores – you need to go to a specialized wholesale supplier of plumbing materials.
Giacomini – Italian standard with a paradox
Italian manufacturers Giacomini and Caleffi mostly use M30x1.5, which would be great – the problem is, however, in the depth and profile of the seat, which can slightly differ from the Central European standard. In practice, most modern heads can be screwed onto Giacomini valves without an adapter, but precise calibration is required after installation, as the valve pin may have a different lift. This topic is covered in a separate article Calibration and adaptation of a programmable head after installation in our Knowledge Center.
Caleffi (M30x1.5 with extended nut)
Caleffi valves have M30x1.5, but the nut is sometimes wider in construction and requires that the adapter or head body has enough space to tighten. Standard heads will fit, but tightening the nut may require an extended wrench or other tools different from those used for a standard Heimeier valve.
Old Soviet / Czechoslovak standard
In panel buildings from the 60s to 80s, you will find valves that do not have standard European threads. These are constructions designed for manual thermostatic heads from the local production of Arizony, Ekolt, or directly from factory production. Their thread may be M26×1, M28×1, or even a special bayonet without a metric thread.
In such cases, there are two options: either find a special adapter (which is becoming increasingly difficult), or it is more economical to replace the entire valve with a modern one – which we recommend in any case, since these valves have no guarantees of sealing or flow regulation after four decades of operation.
How an adapter works and when you need it
An adapter for a thermostatic head is a simple intermediate component – it has the geometry required for a specific type of valve on one side and a standard M30x1.5 thread on the other side, which the head accepts. In principle, it bridges the difference between a proprietary system (Danfoss, Caleffi special, Herz special, etc.) and the standard head interface.
You do not need an adapter if:
- Your valve has M30x1.5 and you are buying a head with M30x1.5 – you can mount it directly.
- The head manufacturer included an adapter in the package – which SALUS does with some models.
You need an adapter if:
- You have a Danfoss RA/RAV/RAVL valve and want to install any modern programmable head on it.
- You have an older valve with a different thread than M30x1.5.
- You want to replace a branded head with another brand, where the original head was proprietary (e.g., original Danfoss head → SALUS or Elektrobock).
Material and quality of adapters
You can find plastic and brass adapters on the market. Plastic ones are cheaper, lighter, and sufficient for regular use – a high-quality polycarbonate adapter will last for years at the typical radiator temperatures (40–80 °C). Brass adapters are more robust, more resistant to long-term heat and mechanical stress, and are the preferred choice for valves where higher vibration or pressure is expected (e.g., floor convectors with more aggressive flow).
Do not buy unbranded adapters from Asian marketplaces without certification – a leak at the thread won’t cause a flood (the adapter is not in direct contact with water), but mechanical instability can cause the head to loosen and the regulation to fail.
Concrete examples from practice – scenarios we see regularly
Scenario 1: Apartment in a new building after 2005, Danfoss valves
This is by far the most common case. The customer lives in an apartment block built or renovated after 2000, where the developer installed Danfoss RA valves (you can recognize them by the characteristic olive or white plastic with a clicking mechanism). The customer buys a SALUS PH 60 or Elektrobock HD10 and finds out that the head cannot be screwed on – the thread simply does not match.
Solution: Danfoss RA → M30x1.5 adapter. This adapter is sold as an accessory with most heads or separately. It is a plastic ring with a bayonet snap-fit at the bottom and a metric thread on top. Procedure: remove the original head (or cover), snap the adapter onto the valve, and then screw the new head onto the adapter in the usual way. The whole replacement takes five minutes.
Scenario 2: Older panel building, unknown valve manufacturer
The customer from a 1970s panel building does not know what kind of valves they have. Description: "They are white, rusty, and no one could tell me what they are." Photographs show valves likely from the former Biotep or Ekolt production, with a non-standard thread of around 26 mm.
Recommended procedure: Do not waste time looking for an adapter. Call a plumber and have the valves replaced with modern ones with M30x1.5 (e.g., Heimeier, Oventrop or Herz) – an investment of around 15–25 € per unit, 150–250 € for ten radiators. After that, you can install any modern head without problems and even improve the system's hydraulic performance.
Scenario 3: Single-family house, Herz valves, replacing manual with programmable
Herz is an Austrian company, very popular in single-family homes. Their valves mostly use M30x1.5, so the customer buys, for example, an Elektrobock EMF-1 and can directly install it without any adapter. This is a pleasant scenario – no surprises.
However, be careful: some older Herz valves (before 1990) had M30x1.5 with a reduced seat depth, which causes the newer head to screw on but the valve pin does not reach full lift. Result: regulation works, but full valve closure may not be perfect. Solution: calibrate the head after installation (details in the article Calibration and adaptation of a programmable head after installation).
Scenario 4: Oventrop valves in an administrative building
Oventrop is a German company with a long tradition. Their valves Uni LH, Uni SH and others mostly use M30x1.5, but some series have their own adapter system. If you encounter Oventrop and nothing screws in, look for the valve marking on the body and identify the correct adapter from the Oventrop catalog based on it.
Table: Thread overview by valve manufacturer
| Manufacturer / valve type | Valve thread | Required adapter | Note |
|---|---|---|---|
| Heimeier (modern) | M30×1.5 | No | Direct mounting |
| Oventrop Uni LH/SH | M30×1.5 | No / depends on series | Check type |
| Danfoss RA / RA-N | Proprietary bayonet | Yes – RA→M30×1.5 | Most common case |
| Danfoss RAV | Proprietary (RAV) | Yes – RAV→M30×1.5 | Different adapter than RA! |
| Danfoss RAVL | Proprietary (RAVL) | Yes – RAVL→M30×1.5 | Low profile |
| Herz (modern) | M30×1.5 | No | Direct mounting |
| Giacomini | M30×1.5 | No | Check pin lift |
| Caleffi | M30×1.5 | No | Direct mounting |
| IMI Hydronic (Drayton) | M30×1.5 / proprietary | Depends on model | Check catalog |
| Old Czech/Slovak manufacturer | M26×1, M28×1 and others | Rarely available adapter | We recommend valve replacement |
| Comap (older) | M28×1.5 | Yes – M28→M30 | Less common |
What happens if you use the wrong adapter or force it to screw on?
This is not an academic question. From practice we know that some customers try to "tighten" the head when the thread does not quite catch. The results are unpleasant:
- Thread stripping: if the diameter is similar but not identical, the thread gets stripped. Result: non-functional valve that needs to be replaced. Cost of unnecessary repair: 50–120 € including plumber's work.
- Fake tightening: the threads seem to catch, but the connection is not secure. The head falls off or loosens after a few days, which can cause the valve to remain either fully open or fully closed.
- Incorrect pin position: an incorrect adapter can cause the valve pin to be pressed at the wrong height, which blocks the valve in one position. The radiator either constantly heats or does not heat at all.
Conclusion: never try to force it. If the thread does not catch smoothly after two turns by hand, it is wrong. A head with M30x1.5 on the correct valve screws on easily, without force, at least three to four turns before tightening.
Adapters included with heads – what the packaging contains
Manufacturers of programmable heads are aware of the diversity of valves and therefore many models come with adapters in the packaging. Let's look at specific cases:
Most Elektrobock models (HD10, HD20, EMF-1) are delivered with a basic coupling nut M30x1.5 and sometimes also with one or two adapters for Danfoss. If the packaging does not include an adapter, it is always clearly stated and the adapter can be purchased separately.
SALUS models (PH 55, PH 60) also include a M30x1.5 nut and documentation with an overview of compatible adapters in the packaging. SALUS has a broader ecosystem of accessories, so all common adapters (Danfoss RA, RAV, RAVL, M28, M32) can be purchased as original accessories directly under the SALUS brand.
If you are sure that your valve is M30x1.5, no adapter is needed and you can proceed directly to installation, which is described in detail in the article Step-by-step installation of a programmable head on a radiator valve.
Tips for measuring and verifying the thread in the field without tools
If you don't have a caliper at hand, there are also improvised methods for verifying the thread:
- Credit card method: A standard credit card is 85.6 mm wide. If the valve takes up roughly a third of the card's width (about 28–30 mm), it is likely M28 or M30.
- Photo for comparison: Take a photo of the valve with a coin next to it as a scale (a 1 euro coin has a diameter of 23.25 mm). From the photo, you can estimate the ratio.
- Verification by screwing: If you have any M30×1.5 bolt (e.g., an old head), try to screw it in – if it fits smoothly, it is M30. If it slips or is too loose, the thread is different.
- Contact atria.sk: If you cannot identify the valve even from a photo, take photos of the entire valve from multiple angles and contact us – we can usually determine the type from the photo.
Special cases: floor heating and convectors
Programmable heads are primarily used on radiator valves, but the topic of threads also concerns other heating system components. On floor heating manifolds, there are valves for actuators (servomotors), not for thermostatic heads – these have a completely different type of connection (M30×1.5 is the same dimension, but the pin function is different).
If you are dealing with a combination of floor and radiator heating, be careful not to confuse thermostatic heads with electric actuators for floor heating manifolds. Both can fit on M30x1.5, but they work on a different principle – the actuator opens and closes the valve with an electric motor without a thermostatic function.
Most frequently asked questions (FAQ)
Is M30×1.5 the same thread for all head manufacturers?
Yes, M30×1.5 is a standard metric thread and is physically the same regardless of whether it is for Elektrobock, SALUS, Danfoss heads or other brands. The 30 mm diameter and 1.5 mm pitch are standardized values. The difference may be in the depth of the threaded hole and in the tolerance, but the connection will be functional between any two components with M30×1.5.
Can I identify the thread by the color or shape of the plastic part of the valve?
Partially yes. Danfoss RA valves have a characteristic olive-green or white plastic body with a visible locking mechanism. Heimeier valves are mostly chrome or white. However, relying solely on color is not enough – the most reliable identification is measurement or finding the manufacturer's label on the valve (sometimes engraved directly on the metal body of the valve).
What if the adapter is not sealing and water is dripping?
The adapter for the thermostatic head does not come into contact with the water inside the heating system – it sits on the external threaded part of the valve, not on the hydraulic seal. If water is dripping from the valve after replacing the head, the problem is not with the adapter, but with the seal of the valve itself – this is a different topic and usually requires replacing the valve seal or the entire valve by an installer.
Can I install a programmable head on a valve without thermostatic preparation?
There are two types of valves: valves with thermostatic preparation (they have a protruding pin that is pressed to regulate flow) and valves without it (classic manual taps). You cannot install a programmable head on a valve without thermostatic preparation – it would regulate nothing. Such a valve needs to be replaced with a valve with thermostatic preparation, which is again work for an installer and requires draining at least part of the system.
I lost the adapter from the package – where can I buy it?
Adapters for common types (Danfoss RA, RAV, RAVL → M30×1.5, or M28→M30) are standard accessories that you can find in our category programmable heads as a separate accessory, or directly from the head manufacturers (SALUS, Elektrobock). The price of one adapter ranges from 2 to 8 € depending on the material and manufacturer.
Do the threads of programmable and manual thermostatic heads differ?
No – the programmable head has the same thread as the manual thermostatic head. Both are designed for the same valve system. If a manual thermostatic head with M30×1.5 worked in a given location, the programmable one will simply replace it without any mechanical changes. This is one of the benefits of standardization, which we discuss in more detail in the article Programmable vs. manual thermostatic head – which one is worth it.
Conclusion – the thread is a detail, but a decisive one
Choosing the right adapter may seem like a minor technical detail, but in practice, it is a step that determines whether the entire installation takes five minutes or ends up with a frustrated customer and a damaged valve. It is essential to identify the manufacturer and type of valve before purchasing the head, or at least verify the thread by measurement.
The vast majority of modern radiator valves in Slovak households fall into two categories: either they have a direct M30×1.5 thread (Heimeier, Herz, Oventrop, Caleffi, Giacomini), or they are Danfoss valves requiring an appropriate adapter. Both situations have simple and available solutions.
If you plan to replace manual heads with programmable ones in a larger number—such as in several rooms or an entire apartment—we recommend starting by checking the valves in each room before placing an order. Sometimes you may encounter two different types of valves in one apartment, for example, if the system was partially renovated. In such cases, you will need adapters for both types, and it is better to know this in advance.
A detailed guide through the entire replacement process—from identifying the valve to running your first weekly program—can be found in the articles Installation of a programmable head on a radiator step by step and Setting up a weekly program on a thermostatic head in our Knowledge Center. A product selection based on features and price is covered in the article How to choose a programmable radiator head—what to pay attention to.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us—we are happy to help.